This invention relates to a dispensing and mixing apparatus and more particularly to a unique and simplified structure which permits a dispensing cartridge to be reused with multiple static mixers. In addition, this invention relates to a cartridge structure which can withstand high extrusion pressure while minimizing the thickness of the walls of the cartridge and which can withstand increased extrusion pressure transmitted by the piston. Furthermore, the cartridge includes chambers shaped to facilitate retaining of the materials within the chambers.
Dispensing and mixing apparatus is well known in the prior art for a variety of pasty or highly viscous products such as adhesives, joint filler agents, foams, sealants and molding compounds. The products typically consist of two or more components stored separately in separate chambers in a cartridge. A plunger is usually advanced against a piston in each chamber to extrude the components through orifices into a disposable static mixer removably coupled to the cartridge. As the components flow through the mixer, they are thoroughly intermixed and a chemical reaction is started between the components which ultimately results in a hardening or solidification of the components when they are inserted into the parts to be sealed.
The solidification takes a predetermined amount of time and as such, the components will solidify in time if left in the static mixer and this will render the static mixer no longer useable. If the components get in contact with each other at the exit end of the chambers in the cartridge or in or on any extension of the chambers after the static mixer is removed, the components being in contact will harden and solidify requiring removal of the solidified material, if possible. Occasionally, such solidified material cannot be removed, making it impossible to reuse the cartridge with another mixer, even though the cartridge has not been used up. This has resulted in wasted material because the cartridges have to be disposed of after each use. In areas where the extruded materials are expensive, such as in the dental field, this waste is particularly undesirable.
There have been attempts to solve the problem of avoiding the hardening of material at the end of the cartridge to prevent rendering the cartridge unsuitable for further use. One example of a highly complex and expensive structure for solving this problem is disclosed in U.S. Pat. No. 5,080,262 issued Jan. 14, 1992. This patent discloses a structure in which two components are stored in separate chambers in a cartridge. As the components are extruded from the cartridge, one component is moved into an annular orifice which surrounds a central cylindrical orifice for the other component. A static mixer is provided which screws into the cartridge and has various walls and edges at different levels and of complex shapes required to mate with complementary walls and edges on the coaxial end of the cartridge to form continuations of the annular orifice and the central cylindrical orifice. The complex structure renders the static mixer very expensive and after each use it may be necessary to dispose of the mixer if the components will harden in the mixer. Additionally, by changing the path of the material in the cartridge from colinear to coaxial requires extra pressure.
U.S. Pat. No. 4,767,026 issued Aug. 30, 1988, describes a dispensing and mixing apparatus in which two components to be mixed are stored in separate chambers in a cartridge. A doubled walled baffle is positioned in a common orifice to keep the components separated as they are extruded into a mixer. However, the mixing takes place at the end of the baffle which is at the edge of the cartridge. Typically, after extrusion for a particular use is completed, the static mixer is retained as a cap until the next use. However, since there is no particular structure to keep the components from mixing at the end of the baffle, the back curing of the components upstream of the static mixer will cause the components to harden and the cartridge will have to be discarded together with any unused materials. This apparatus is typical of many prior art in that a thin separation baffle is housed in the cartridge between the component holding chambers and wherein the mixing of the two components occurs at the end of the baffle which is at the end of the cartridge.
The cartridges are typically made of plastic material which is always porous to some extent, and therefore gases and moisture slowly permeate through the outer walls of the plastic cartridges into the chambers. Certain components such as those used in dentistry are contaminated by such gases and are highly reactive to moisture. The greater the exposed surface area of the cartridge, the greater the amount of gas and moisture that will enter the chamber by a given wall thickness.
Additionally, with the continuous pressure applied by the piston, the walls of the cartridge may tend to deflect. In order to combat this deflection, the walls of the chambers are typically made relatively thick. The plastics used are not generally biodegradable and are an environmental problem since the cartridges are not recycled.
In addition, in high pressure extrusion, there is often leakage of the components around the piston which limits the pressure available. Furthermore, the leakage can render the device used to advance the pistons unusable for further applications.
Also, the coupling arrangement between the static mixer and the cartridge was often complex requiring screw threads or clamping arrangements. This provided for time lost in making quick connections and prevented the ability to easily use static mixers with existing cartridges.
In view of the foregoing, a simplified structure which permits the reuse of a cartridge would be very beneficial. These improvements would be particularly beneficial if the cartridge had unique features such as increased strength to withstand deflection under pressure, while at the same time the weight and thickness of the cartridge is maintained at a minimum. In addition, the ability to readily withstand high extrusion pressures without component leakage would be very desirable as would an improved coupling arrangement between the static mixer and the cartridge.